Radio communication system using multi-antenna transmission technique, and multi-user scheduler therefor

ABSTRACT

A transmitting station in the radio system performing scheduled transmission to a plurality of user terminals including: a plurality of antennas and a reception unit configured to obtain reception quality information estimated from a pilot channel among information fed back from each of the plurality of user terminals, to determine based on the obtained reception quality information, a transmission system for the plurality of antennas and a transmission unit configured to add a specific bit which identifies the determined transmission system to a scheduler management channel, and to vary contents of the other bit area in the scheduler management channel, as corresponding to the specific bit, and further transmit the scheduler management channel to the plurality of user terminals.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a Divisional of U.S. application Ser. No.12/186,209, filed on Aug. 5, 2008, now pending, which is a continuationof International Application No. PCT/JP2006/302174, filed on Feb. 8,2006, the contents of each are herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a radio communication system using amulti-antenna transmission technique, and a multi-user scheduler to beapplied thereto.

BACKGROUND ARTS

In the radio communication, as a technique of using a plurality oftransmission and reception antennas (multi-antenna), there have beenstudied a technique of transmission by a multiplicity of antennas andreception by a multiplicity of antennas (MIMO: Multi Input Multi Output)in which different streams are transmitted from each antenna, therebyimproving throughput, and a beamforming (which may be represented as BFhereinafter in an appropriate time) technique in which multiplextransmission is performed by weighting an identical stream, therebyimproving reception quality (Non-patent document 1).

Further, in Patent document 1, in a mobile communication system having aplurality of antennas, in order to improve spatial efficiency, there hasbeen disclosed a method of adaptively performing switching control in amixed environment of space multiplexing (SDM: Space Division Multiplex,SDMA: Space Division Multiplex Access), according to a traffic conditionin a communication area.

However, conventionally, the MIMO multiplexing and beamforming have beenrecognized as independent techniques because of the passage of differentpropagation paths, and a study taking mutual fusion into considerationhas hardly been made.

Namely, in the beamforming mode, because transmission weighting is made,a passing propagation path is different from that in the MIMOmultiplexing, and accordingly, it is difficult to simultaneously controlboth methods using a single common pilot. Therefore, the necessity ofseparate pilots has been studied. As a result, in any of theabove-mentioned documents, there is neither disclosure nor suggestionabout a concrete structure of controlling switching between the MIMO(SDM is also included in MIMO) and the beamforming.

[Non-patent document 1] “Spectral Efficiency of Wireless Systems withMultiple Transmit and Receive

Antennas”, F. R. Farrokhi et al., PIMRC2000 vol. 1 page 373-377.

[Patent document 1] the official gazette of the Japanese UnexaminedPatent Publication No. 2004-201296.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

From the above viewpoint, the present invention has been invented fromthe viewpoint of adaptively choosing the use of MIMO multiplexing andbeamforming techniques. It is an object of the present invention toprovide a concrete method for effectively fusing a scheduler managementchannel used in adaptive modulation with a multi-antenna transmissiontechnique, and a radio communication system using the above method.

Further, it is another object of the present invention to provide aradio communication system capable of switching MIMO among multiplexing,beamforming and transmission diversity to save energy when informationamount to be transmitted is small, to obtain stable communication whencommunication condition is severe due to the vicinity of a cell edge inmobile communication, and to optimize communication when correlationexists in the propagation paths.

Means to be Solve the Problems

As a first aspect of the present invention to achieve the aforementionedobjects, a transmitting station in a radio system performing scheduledtransmission to a plurality of users from the transmitting stationhaving a plurality of antennas is disclosed. The above transmittingstation obtains reception quality information estimated from a pilotchannel among information fed back from the plurality of users, andbased on the obtained reception quality information, determines atransmissions system whether to perform MIMO multiplexing, whichtransmits data of different streams from the respective plurality ofantennas, or to perform beamforming, which transmits an identical streamdata by weighting each of the plurality of antennas, and further,transmits the information identifying the determined transmission systemto the user side by adding to a scheduler management channel.

In the above first aspect, the information to identify the determinedtransmission system to be added to the scheduler management channel isconstituted of a specific bit, and corresponding to the specific bit, aformat of the other bit area in the scheduler management channel isvaried.

Further, when the determined transmission system is beamforming,corresponding to the specified bit added to the scheduler managementchannel, weight information to the plurality of antennas or weightinformation of a plurality of reception antennas is reported using theother bit area.

As a second aspect of the present invention to achieve theaforementioned objects, a transmitting station in a radio systemincludes: a plurality of antennas; a memory storing information of aplurality of users; a first modulation section adaptively modulating theuser information output from the memory; a time-division conversionsection performing time-division multiplexing of the user informationoutput from the memory, and a second modulation section adaptivelymodulating the each time-divided output; corresponding to the pluralityof antennas, a plurality of radio signal generation sections supplyingoutputs of the first modulation section and the second modulationsection to the plurality of antennas; a reception section obtainingreception quality information estimated from a pilot channel amonginformation fed back from the plurality of users; and based on thereception quality information obtained in the reception section, ascheduler determining a transmission system whether to performbeamforming, which transmits an identical stream data by weighting eachof the plurality of antennas or to perform MIMO multiplexing, whichtransmits data of different streams from the respective plurality ofantennas. Further, the above scheduler controls to validate the outputof the first modulation section when performing the beamformingtransmission, and to validate the output of the second modulationsection when performing the MIMO multiplexing transmission.

Further, as a third aspect of the present invention to achieve theaforementioned objects, in a radio system performing scheduledtransmission to a plurality of receiving stations from a transmittingstation having a plurality of antennas, a transmitting station obtainsreception quality information estimated from feedback informationobtained from the plurality of receiving stations, and determines atransmission system whether to perform beamforming transmission, whichtransmits data of an identical stream by weighting each of the pluralityof antennas based on the obtained reception quality information, or toperform MIMO multiplexing transmission, which transmits data ofdifferent streams from the respective plurality of antennas, andtransmits information to identify the determined transmission system byadding to a scheduler management channel. Further, from the aboveidentification information in the scheduler management channel, each ofthe plurality of receiving stations decides a decoding algorithmdepending on either a beamformed transmission signal or a MIMOmultiplexed transmission signal. Further, according to the decideddecoding algorithm, in case of the MIMO multiplexed transmission signal,each receiving station demodulates by obtaining the modulation systemfrom the information in the scheduler management channel, using achannel estimation value estimated from the pilot channel, while in caseof the beamformed transmission signal, based on the weight informationadded to the scheduler management channel, each receiving stationperforms signal synthesis between the plurality of antennas and channelcompensation by performing optimal reception weighting.

In the second aspect, it is possible to configure such that an uplinkand a downlink channel between the transmitting station and thereceiving station are divided with different carrier wave frequencies,and further, the receiving station transmits to the transmitting stationa channel matrix estimated from the received pilot signal and a signalto integrated noise ratio on the basis of each of the plurality ofantennas, as the feedback information.

Further, the above transmitting station may obtain a zero forcing (ZF)solution from the channel matrix fed back from the receiving station,calculate the ZF solution, and reflect only either an obtainedtransmission weight Wtx or a reception weight Wrx in the schedulermanagement channel.

Still further, when the transmission weight Wtx obtained from thescheduler management channel is transmitted, it is also possible toconfigure such that the receiving station obtains a reception weight Wrxof a Minimum Mean Square Error(MMSE) solution, using the channelestimation value obtained from the received pilot, and using theobtained reception weight Wrx, the receiving station performs signalsynthesis in regard to the plurality of antennas.

Further, in the second aspect, the receiving station calculates a zeroforcing (ZF) solution from a channel matrix estimated from the receivedpilot signal, and transmits the obtained transmission weight Wtx andchannel quality information of beamforming to the transmitting station,as the feedback information.

Also, in the second aspect, the receiving station transmits to thetransmitting station a transmission weight Wtx obtained by calculating azero forcing (ZF) solution from a channel matrix estimated from thereceived pilot signal or transmission direction information obtainedfrom the peak of a beam pattern in a power concentration directiongenerated from the obtained transmission weight Wtx, as the feedbackinformation.

Further, the transmitting station generates the beam pattern so thatpower is concentrated in a transmission direction fed back from thereceiving station, and reflects the transmission weight Wtxcorresponding to the beam pattern in the scheduler management channel.

Still further, in the second aspect, an uplink and a downlink channelbetween the transmitting station and the receiving station aretime-divided with an identical carrier wave frequency, and thetransmitting station obtains a channel matrix by correcting a powerdifference between the transmitting station and the receiving station inregard to a channel estimation value from the receiving station to thetransmitting station, and calculates a ZF solution from the obtainedchannel matrix, so as to generate a reception weight Wrx or atransmission weight Wtx.

Further, it is possible to configure the receiving station to obtain areception weight Wrx of a Minimum Mean Square Error (MMSE) solution,using the transmission weight Wtx obtained from the scheduler managementchannel and the channel estimation value obtained from the receivedpilot channel, and to perform signal synthesis in regard to theplurality of antennas using the obtained reception weight Wrx.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram illustrating a simplest example of multi-antennatransmission.

FIG. 2 shows a diagram explaining transmission (omni transmission) of apilot channel A and scheduler management channel B to the overall cells.

FIG. 3 shows a diagram illustrating an exemplary configuration of ascheduler management channel B according to the present invention.

FIG. 4 shows a diagram illustrating a case that a decision bit X in anarea I of a scheduler management channel B specifies MIMO multiplexing(a).

FIG. 5 shows a diagram illustrating a case that a decision bit X in anarea I of a scheduler management channel B specifies beamforming (b).

FIG. 6 shows a diagram illustrating a schematic configuration of atransmitting station to which the present invention is applied.

FIG. 7 shows a diagram illustrating the conventional example using aseparate channel.

FIG. 8 shows a diagram explaining a method of reporting a transmissionweight w when performing transmission beamforming.

FIG. 9 shows a diagram illustrating an example of an antenna radiationangle.

FIG. 10 shows a diagram explaining a transmitting station in anexemplary implementation listed as a group 1 of Table 1, as anembodiment 1.

FIG. 11 shows a diagram explaining a receiving station in an exemplaryimplementation listed as a group 1 of Table 1, as an embodiment 1.

FIG. 12 shows a diagram explaining input information to a scheduler in atransmitting station.

FIG. 13 shows an exemplary configuration of a scheduler.

FIG. 14 shows a diagram illustrating a scheduler processing flow.

FIG. 15 shows a diagram illustrating an exemplary configuration of atransmitting station corresponding to an embodiment 2 corresponding to agroup 2 in Table 1, as an embodiment 2.

FIG. 16 shows a diagram illustrating an exemplary configuration of areceiving station corresponding to the transmitting station of anembodiment 2 corresponding to a group 2 in Table 1.

FIG. 17 shows a diagram explaining a transmitting station in anembodiment 3 corresponding to a group 3 in Table 1.

FIG. 18 shows a diagram explaining a corresponding receiving station inan embodiment 3 corresponding to a group 3 in Table 1.

FIG. 19 shows a diagram explaining a corresponding transmitting stationin an embodiment 4 corresponding to a group 4 in Table 1.

FIG. 20 shows a diagram explaining a corresponding receiving station inan embodiment 4 corresponding to a group 4 in Table 2.

FIG. 21 shows a diagram explaining a corresponding transmitting stationin an embodiment 5 corresponding to a group 5 in Table 2.

FIG. 22 shows a diagram explaining a corresponding receiving station inan embodiment 5 corresponding to a group 5 in Table 2.

FIG. 23 shows a diagram explaining a corresponding transmitting stationin an embodiment 6 corresponding to a group 6 in Table 2.

FIG. 24 shows a diagram explaining a corresponding receiving station inan embodiment 6 corresponding to a group 6 in Table 2.

FIG. 25 shows a diagram illustrating another configuration of ademodulation section and thereafter, in a receiving stationcorresponding to antenna data stream retransmission control.

PREFERRED EMBODIMENTS MODE FOR CARRYING OUT THE INVENTION

The preferred embodiment of the present invention is describedhereinafter referring to the charts and drawings. However, it is notedthat the embodiments aim at better understanding of the presentinvention, and accordingly, the technical scope of the present inventionis not limited to the embodiments described below.

Now, for the sake of understanding of the present invention, fundamentalfeatures of the present invention will be described first. Additionally,for simplifying the description and easy understanding, a packet-basedmobile communication system is considered here as a radio communicationsystem, and as a simplest channel structure, only pilot channel,scheduler management channel and data channel are dealt with as anexample.

Further, in the description hereafter, as a simplest example ofmulti-antenna transmission, the description is made taking an example oftransmission using two antennas

ANT1, ANT2, as shown in FIG. 1. However, it is possible to performsimilar control in case of transmission using a plurality M of antennasmore than and inclusive of two (M≧2).

In FIG. 1, a notation A in a transmission channel format CF forwardedfrom the antennas ANT1, ANT2 represents the pilot channel, and anotation B represents the scheduler management channel, and a notation Crepresents the data channel.

Here, as shown in FIG. 2, it is necessary to transmit the pilot channelA and the scheduler management channel B to an overall cell (omnitransmission). Further, as to the pilot channel A, to avoid interferencebetween transmission antennas 1, 2, transmission is performed afterorthogonalizing each code or time-frequency. Similarly, as to thescheduler management channel B of which transmission is also required tothe overall cell, either orthogonalized transmission is performed orreception is performed by use of a technique such as most likelihooddetection (MLD).

Further, in regard to the above two transmission channels (pilot channelA and scheduler management channel B), it is necessary to receiveerror-free even at a cell edge.

In contrast, according to the present invention, it is decided whetherthe MIMO multiplexing transmission or the beamforming is to be made,from reception quality information (CQI: Channel Quality Indicator)estimated from the pilot channel A, with attention directed to the datachannel C which is transmitted to only a scheduled user.

According to the control in the present invention, MIMO multiplexing isperformed when correlation between transmission antennas is low in anarea near the self-cell with a good SINR (Signal to Interference andNoise Ratio), so as to improve a throughput. Oppositely, beamforming isapplied in an area either having a poor SINR near a cell edge or havinghigh correlation between transmission antennas, so as to increaseasignalgain. Thus, as a feature, the throughput (communication amount) andcoverage (communicable range) are improved.

Additionally, it may also be considered to decide whether to performcoded transmission diversity or beamforming by measuring spacecorrelation of the transmission antennas.

In the following embodiments, only an exemplary case of switchingbetween MIMO multiplexing and beamforming is dealt with.

FIG. 3 shows a diagram illustrating an exemplary configuration of ascheduler management channel B according to the present invention. As afeature, in a partial area I of the scheduler management channel B,there is inserted a decision bit X to specify whether to perform MIMOmultiplexing or beamforming. Here, the decision bit X is not necessarilyplaced at such the top area of the channel as shown in FIG. 3. Referringto FIGS. 4, 5, the following describes that contents Y signified by bitsin other areas are changed as a result of the decision of the abovedecision bit X.

FIG. 4 shows a diagram illustrating a case that a decision bit X in anarea I of the scheduler management channel B specifies MIMO multiplexing(a). In case of the MIMO multiplexing, there are two data streams to betransmitted by the antenna ANT1 and the antenna ANT2, and a controlinformation amount is included in an area II to specify adaptivemodulation according to the two streams.

FIG. 5 shows a diagram illustrating a case that a decision bit X in thescheduler management channel B specifies beamforming (b). As contrastedwith the MIMO multiplexing, in case of the beamforming, data to betransmitted is one stream, and a less control information amount ofspecifying adaptive modulation is needed. As such, the decision bit X ofMIMO multiplexing or beamforming is defined, and according to thedecision thereof, the signification of other bits is changed.

Also, in the area having a reduced control image amount in case of thebeamforming, there is provided a designation (c) for appropriatelyreporting either a transmission weight of the beamforming oralternatively, a transmission weight and a reception weight for areceiver.

As such, according to the present invention, based on the decisionresult of the decision bit X added to the partial area I in thescheduler management channel B, it is possible to switch over betweenthe MIMO multiplexing and the beamforming instantaneously.

FIG. 6 shows a diagram illustrating a schematic configuration of atransmitting station to which the present invention is applied.

The configuration shown in FIG. 6 is applicable to a transmittingstation having multi-antennas (two antennas ANT1, ANT2, as an example)when transmitting by scheduling a plurality of users. As one example ofthe system, the transmitting station corresponds to a base station in amobile telephone system, and a downlink for transmission therefrom tothe plurality of users (mobile terminals) is assumed.

As to the plurality of users, user 1 to user n, being in communicationwith a certain transmitting station, necessary information is collectedfrom the Internet, etc. The collected user 1 information to user ninformation is temporarily cached into a position corresponding to theuser i in a memory 10 of the transmitting station.

According to a transmission request from a scheduler 100, datatransmission is prepared. In FIG. 6, there is depicted a schematicdiagram illustrating that, at certain timing in a certain band, atransmission request to the user i is made and either MIMO multiplexingor beamforming is selected. The above selection is determined inreflection of a pre-trained propagation path condition.

Now, in case the MIMO multiplexing is selected, data for two streams areread out from memory 10, and by means of a serial-to-parallel (S/P)converter 11, the data are split into each information amount to betransmitted from each antenna (ANT) 1, 2. Then, on the basis of eachsplit information amount, coding and modulation (adaptive modulation)corresponding to each propagation environment from the antennas ANT1,ANT2 are performed in adaptive modulators 12 ₁, 12 ₂.

Because the adaptively modulated signals are mutually different signals,the signals are converted into radio frequencies and radiated from theantennas ANT1, ANT2 without being weighted. The chart depicted withdotted lines from the antennas ANT1, ANT2 is MIMO multiplexing radiationpatterns.

On the other hand, in case the beamforming is selected, a data for onestream is read out from memory 10, and a signal being adaptivelymodulated in an adaptive modulator 13 is copied in a copying section 14,which is thereafter weighted so that a directivity gain is directed tothe user, and then radiated from the antennas ANT1, ANT2. Each weight isobtained from pre-trained transmission path information. The solid linedepicted toward the user i from the antennas ANT1, ANT2 is a beamformingradiation pattern.

Thus, scheduler 100 is configured to specify a variety of modes on thebasis of the trained propagation path information.

Next, the merits of reporting the weight in transmission/receptionbeamforming proposed in the present invention are described.

In the conventional example, when performing transmission beamforming,in addition to a common pilot to be transmitted to the overall cell, itis generally performed to insert a separate pilot for a certain user.Using FIG. 7, the conventional example using a separate channel isdescribed.

In FIG. 7, d(t) is a data for a certain user, w₁, w₂ are weights forbeamforming to the certain user, p_(c1)(t), p_(c2)(t) are orthogonalcommon pilots to be inserted antenna-by-antenna, and h₁(t), h₂(t) arepropagation paths from the antennas ANT1, ANT2 to the certain user.Further, each separate pilot is represented as p_(d1)(t), p_(d2)(t).

Additionally, to simplify the notations, in regard to the above FIG. 7,a case of a single reception antenna is depicted, and however, noparticular problem arises if the number of antennas is increased. Also,as to the weight W, no notation of time t is shown. The reason is thatif there is a high spatial correlation, tracking the weight W comes togreatly depend on the angular velocity of a user position, and thetransmission direction is not varied in an instantaneous time variationin fading. Reversely speaking, if the spatial correlation is low,dependency on time t occurs.

In order to make each separate pilot pass through the same propagationpath of the independent user data, the insertion thereof into the sameresource of the data is required. Also, in order to perform propagationpath estimation including the fading by means of the above separatepilot, a notation of time t is given.

When looking at the source of channel estimation, at a moment when thereis no separate pilot, it is not possible to decode data because a fadingvariation is not known.

Next, using FIG. 8, there is described a method of reporting atransmission weight w when performing transmission beamforming.

The configuration is the same as illustrated in FIG. 7, and however,according to the present method, by reporting transmission weights w₁,w₂ to a receiver, a propagation path on which data have been passedthrough is estimated in combination with the common pilot.

The basic principle is that channel information through spacepropagation from the respective antennas ANT1, ANT2 can be estimatedusing the common pilot, and that if the weight information of eachantenna is known further, the propagation path on which data have passedcan be estimated.

Further, if the spatial correlation between the transmission antennasANT1, ANT2 is high, the fading variation between the transmissionantennas is looked similar, and therefore, optimization of the weightbecomes an issue which can be solved by tracking using the angularvelocity of the receiver looked from the transmission antenna.Therefore, differently from the separate pilot, the data can be decodedeven when the weight information is decimated to a certain extent.

Alternatively, it is also possible to improve information accuracy ofthe transmission weight by decimating transmission opportunities andadding redundancy. Further, because the channel response tracking thefading can be obtained by the common pilot having large transmit power,it is possible to perform channel estimation with high accuracy.

Thus, the merits of the beamforming of a weight report type are greatand flexible because it is possible to report the weight according tothe adaptive modulation.

Next, in regard to pre-trained channel information and informationnecessary to feedback, description of FDD (Frequency Division Duplex)and TDD (Time Division Duplex) are made separately.

First, the description is started from the FDD. Because a transmissionlink for propagating from a transmitting station to a receiving stationhas a different carrier wave frequency from a reception link forpropagating from the receiving station to transmitting stationequipment, it is useless for the transmission link if a channelestimation value of the reception link is trained. In regard to fourcombinations of information to be fed back at this time, description ismade using Table 1.

TABLE 1 Combination of feedback information (FDD) Information from Wrxfor the Feedback from the the transmitting receiving Group receivingstation station station 1 Channel matrix H Obtain an optimal Apply theweight, and report reported W_(rx) information 2 Obtain an optimalCalculate by the weight, and report MMSE criterion W_(tx) 3 Optimalweight W_(tx) Inform of W_(tx) Recalculate by CQI at the time of (*1)the MMSE BF criterion (*2) 4 Quantized Inform of W_(tx) Calculate by theinformation of MMSE criterion the optimal weight W_(tx) CQI at the timeof BF MMSE (Minimum Mean Square Error) CQI (Channel Quality Indicator:represented by quantizing the propagation path quality using aparticular rule)

In the above Table 1, the combination groups 1, 2, are a method suchthat a channel matrix H estimated from the common pilot received fromthe transmitting station is calculated in the receiving station side,and the above calculation result is fed back to the transmitting stationside.

From the transmitting station receiving the channel matrix H, in thegroup 1, a reception weight obtained by expressions (7), (8), which areshown in the background theory explained later, is reported using thearea of the scheduler management channel B, and the receiving stationdemodulates the information carried by being beamformed from the abovereported information.

The group 2 is a method such that the transmission weight obtained fromexpressions (7), (8) is reported, and however, by considering apropagation path variation due to a delay before the beamformedinformation is actually carried and the noise condition in a receiver, areception weight of an optimal MMSE minimization criterion is calculatedfrom the transmission weight and the channel estimation value of thecommon pilot at that moment, so as to demodulate. With this, timetrackability and noise tolerance can be improved.

In the group 3, when the entire information of the channel matrix H isfeedback transmitted from the receiving station, a link capacity fromthe receiving station to the transmitting station is greatly consumed.Therefore, considering such inconvenience, the receiver side calculatesan optimal transmission weight obtained from expressions (7), (8), tofeed back the above value W_(tx). By modifying the feedback amount froma matrix type into a vector type, the reduction of the link capacityfrom the receiving station to the transmitting station can besuppressed.

From the transmitting station, the reported transmission weight isreported through the scheduler management channel B, and in regard tothe information, beamforming transmission thereof is performed after theweight is added.

Additionally, in the above Table 1, as an item shown as (*1), if theweight reported from the receiving station is applied at all times, andif the optimal transmission weight fed back is continued to be stored inthe receiving station, reception can be made without the weightinformation through the scheduler management channel B.

Also, by the reception weight calculation in the receiving station, asdescribed in regard to the group 2, the reception weight of the MMSEminimization criterion is obtained with the consideration of the timetrackability and noise tolerance, and by the use thereof, decoding canbe performed.

Additionally, in Table 1, as an item shown as (*2), if the receptionweight at the time of calculating the optimal transmission weight firstis continued to be stored and if a characteristic deterioration isallowed to some extent, reception can be made without obtaining thereception weight of the MMSE criterion again. By this, the calculationamount can be reduced.

The group 4 is intended to further reduce the feedback amount on thelink from the receiving station to the transmitting station performed inthe group 3. To the transmission weight W_(tx) obtained from expressions(7), (8) in the receiving station side, the method is to convey a gainpeak direction of a beam pattern generated using the weight concerned.By reporting only an important point at which transmission beamformingenergy is concentrated, it is possible to drastically reduce thefeedback by aggregating information of only one transmission direction,as contrasted to the group 3 transmitting weight information for thenumber of transmission antennas.

Namely, by modifying the feedback amount from a vector type to a scalartype, it becomes possible to suppress reduction of link transmissioncapacity from the receiving station to the transmitting station.Additionally, if the correlation between the transmission antennas ishigh, the method of interest becomes greatly effective because qualitydeterioration is not so largely produced even the weight information forthe number of transmission antennas is aggregated into one transmissiondirection.

Further, as a means for further information compression, in the methodof the group 4, when an optimal transmission direction is obtained as,for example, 43°, by setting a rule in advance such that thequantization step in the transmission direction is defined at theintervals of 8°, the approximation value of 40° is obtained.

For example, as shown in FIG. 9, illustrating an example of an antennaradiation angle, if the antenna is configured of three sectors of 120°each, the transmission direction is 15 states, and the entiretransmission weights of the transmission antenna can be determined byuse of only 4 bits. As such, it is also possible to considertransmission by quantizing the scalar value of the information amount tobe fed back.

In the transmitting station, the weight is generated based on thereported transmission direction. From the transmitting station, anactually applied weight is reported using the scheduler managementchannel B. The receiving station then calculates a reception weight ofthe optimal MMSE criterion using the above information and the channelestimation value of the common pilot at that moment, so as todemodulate.

Thus, in case of the FDD, it is possible to perform beamforming controlusing any one suitable method from among the four groups of feedbackmethods listed in Table 1.

Next, description is made on the case of TDD. An identical frequencyband is used for both a transmission link and a reception link. Since itis possible to make use of a channel estimation value of the receptionlink through training in the receiving station for the transmission linkin the transmitting station, information to be fed back from thereceiving station to the transmitting station can greatly be reduced.Further description is made using Table 2.

TABLE 2 Combination of feedback information (TDD) Calculation in Reportfrom the the transmission transmission Receiving Group station Stationstation Wrx 5 Channel matrix H Obtain an optimal Apply the weight andreport reported W_(rx) information 6 Obtain optimal Calculate usingweight MMSE criterion and report W_(tx)

Additionally, to apply the channel matrix from the receiving station tothe transmitting station to the direction from the transmitting stationto the receiving station, the difference between the transmission powerin the transmitting station and the transmission power in the receivingstation is corrected, so as to be regarded as substantially equivalent.

In both the groups 5, 6, a channel matrix H from the transmittingstation to the receiving station is estimated using the channel matrixestimated from the pilot channel, transmitted from the receiving stationto the transmitting station, and the correction information, such as thetransmission power difference between the transmitting station and thereceiving station.

From the channel matrix thus obtained, an optimal transmission weightand a reception weight are calculated by solving the expressions (7),(8) described later. Here, in the group 5, the above optimal receptionweight is reported, and in the receiving station, beamformed informationis demodulated using the above information.

In the group 6, the transmission weight obtained from expressions (7),(8) are reported, while the reception weight is not reported. Tocalculate the reception weight in consideration of the actualpropagation channel condition from the transmitting station to thereceiving station and a receiver noise, the optimal reception weight ofthe MMSE criterion is calculated using the channel estimation value ofthe common pilot at that moment and the transmission weight, so as todemodulate. Thus, it is possible to further improve noise tolerance,etc., as compared to the group 5.

Now, to understand the above description, a background theory will bedescribed.

Assuming a certain user reception condition, a signal receptioncondition at a certain moment is expressed by expression (1). A vector xrepresents a transmission signal.

[1]

y(t)=Hx(t)+n(t)   (1)

Each element of H produces a mutually independent multipath. Here, if itcan be regarded that the propagation path condition is invariable withinthe time in which orthogonal pilots spread across a plurality of symbolsare used, expression (2) is led.

[2]

Y(t)=HP(t)+N(t)   (2)

Here, each element of P(t) signifies a transmission antenna number inthe row direction, and transmission timing of the column direction.Further, P(t) has the following property because of being an orthogonalpilot. Here, normalization is performed so as to form a unit matrixafter the calculation of self-correlation.

[3]

P(t)P(t)^(II) =P(t)^(II) =P(t)=I . . . P(t)^(II) =P(t)⁻¹   (3)

Utilizing the above property, a channel estimation value is obtained. Byperforming the processing as shown by expression (4) in a section havingcorrelation in the propagation path, the second term signifying noise issuppressed.

[4]

Ĥ=Y(t)P(t)^(H) =HP(t)P(t)^(H) +N(t)P(t)^(H) =H+N(t)P(t)^(H)   (4)

Next, let the transmission signal to be d(t), then the receptioncondition when beamformed with the transmission weight W, and thereception weight W, is represented as shown by expression (5).

[5]

r(t)=w ^(H) _(rx) Hw _(tx) d(t)+w ^(H) _(rx) n(t)   (5)

Here, the known information on the reception side is the receptionweight W_(rx) obtained by the MMSE criterion, etc. and the channelestimation value;

[6]

Ĥ(≈H)

As to the unknown transmission weight W_(tx), it is necessary to beinstructed from the transmitting station. Feeding back the abovetransmission weight W_(tx) by the scheduler management channel B is oneof the features of the present invention.

Next, a generation method of the transmission weight W_(tx) isdescribed. The above channel estimation value capable of estimated in aterminal is used. In the terminal, since noise influence to be generatedin future is not predictable, the transmission signal weight W_(tx) isto be generated by ZF (Zero Forcing; for use in the equalization of aself-signal, etc.), and the expected reception at that time is as shownby expression (6).

[7]

{circumflex over (r)}(t)=w ^(H) _(rx) Ĥw _(tx) d(t)   (6)

To maximize the reception power in the receiving station, it issufficient if the algorithm shown in expression (7) is solved.

$\begin{matrix}\lbrack 8\rbrack & \; \\\left. {\arg \; {\max\limits_{w_{tx},w_{rx}}\left\lbrack {w_{rx}^{H}\overset{\Cap}{H}{w_{tx}\left( {w_{rx}^{H}\overset{\Cap}{H}w_{tx}} \right)}^{*}} \right\}}} \right\rbrack & (7)\end{matrix}$

-   -   * is complex conjugate

Here, as a restraint condition of a constant transmission power and arestraint condition of a reception weight, attention is to be paid onexpression (8).

$\begin{matrix}\lbrack 9\rbrack & \; \\{{{\sum\limits_{i = 1}^{z}{w_{tx}w_{tx}^{H}}} = {const}}{{\sum\limits_{i = 1}^{z}{w_{rx}w_{rx}^{H}}} = {const}}{{const} = 1}} & (8)\end{matrix}$

Additionally, an ideal solution of the algorithm shown in expression (7)is a value in which the transmission and reception weighting is made sothat the signal is directed to either an orthogonal space having amaximum proper value of the self-correlation matrix obtained from thechannel matrix or an orthogonal space having a largest singular valueobtained from SVD of the channel matrix.

Also, as to the MMSE solution of the beamforming, based on

[10]

Ĥ

estimated as a pre-reported transmission weight W_(lx), a solutionW_(rx) given by the following expression (9) is to be obtained.

$\begin{matrix}\lbrack 11\rbrack & \; \\{{\arg \; {\min\limits_{w_{rx}}\left\lbrack {{1 - {w_{rx}^{H}{Hw}_{tx}}}}^{2} \right\rbrack}}{{wherein},{{\sum\limits_{i = 1}^{z}{w_{rx}w_{rx}^{H}}} = {{{const}{const}} = 1}}}} & (9)\end{matrix}$

Next, concrete embodiments in the cases of FDD and TDD listed in aboveTable 1 and Table 2 will be described.

Embodiment 1

As an embodiment 1, the description is made in regard to a transmittingstation in the implementation example listed as a group 1 of Table 1 asshown in FIG. 10, and in regard to a receiving station as shown in FIG.11.

[Transmitting Station]

In a transmitting station communicating with a plurality (n) of users,the data of the above plurality (n) of users are stored in advance in(n) memories 10 ₁-10 _(n).

There is a mechanism of reading out data from memories 10 ₁-10 _(n)according to a request from a scheduler 100. Here, from the receivingstation (refer to FIG. 11) of each user, feedback information isreturned so as to report space propagation path information and thevalidity/invalidity of the transmitted data.

Scheduler 100 is operated by totaling the above information for theentire users. In FIG. 10, only a feedback information reception section110 for one user is shown.

For example, an example of time multiplexing of each channel is shown inFIG. 10 and thereafter. Additionally, multiplexing of each channel isnot limited to the time multiplexing if only orthogonal multiplexing ismade.

The signal transmitted from the receiving station is down-converted intoa baseband in a reception radio frequency (RF) section 111. Next, bymeans of an S/P (serial-to-parallel) conversion section 112, eachtime-multiplexed channel is extracted, and then a propagation pathvariation is obtained in a channel estimation section 113, using a pilotchannel separate for each user. Compensation for the obtainedpropagation path variation is performed in a demodulation section 114.

Additionally, when error correction processing is made, a decodingsection is required following demodulation section 114. Next, from amongthe data demodulated in demodulation section 114, feedback informationis extracted in a feedback information section 115, from which CQI andACK (acknowledge)/NACK (not acknowledge) information 115 a, which isrequired for adaptive modulation system already performed, and channelmatrix information 115 b transmitted from the transmitting station tothe receiving station are obtained.

A channel matrix H in the above channel matrix information 115 b isinformation necessary for performing transmission beamforming. Further,from the channel matrix H, an optimal ZF solution 115 c obtained fromthe above expressions (7), (8) is obtained.

In the group 1, transmission/reception weight vector information Wrx andCQI at bit forming (BF-CQI) obtainable from expression (13) shown beloware selected, and carried to scheduler 100 after being multiplexedtogether with CQI and ACK/NACK information 115 a in a multiplexingcircuit 116.

In scheduler 100, information from the receiving station correspondingto each of the plurality of users is aggregated, and transmissionpriority is determined in consideration with a space propagationcondition known from the individual CQI, a retransmission conditionknown from the ACK/NACK, a data amount retained in memories 10 ₁-10_(n), etc.

Also, from the CQI, a transmittable maximum data amount is obtained.Then, in regard to a user i having obtained a right to transmit, it iscontrolled to read out the transmittable maximum number of data frommemory 10 _(i) in which the data concerned is stored, via a MIMOmultiplexing/beamforming selection & AMC set section 101.

In MIMO multiplexing/beamforming selection & AMC set section 101, thereare set MIMO multiplexing or beamforming and coding and modulationsystems appropriately modified according to the propagation condition.

Finally, user allocation information, MIMO multiplexing/beamformingselection information, adaptive modulation information, etc. having beenset in AMC set section 101 are forwarded to scheduler managementinformation generation section 102.

When the data are read out from memories 10 ₁-10 _(n), next, in an MAS(multi-antenna system) selection section 113, whether to performtransmission by beamforming or MIMO multiplexing is selected accordingto MIMO multiplexing/beamforming selection and the set information inAMC set section 101. As the criterion thereof, sufficiently, it may bedecided to perform beamforming if the CQI value is relatively bad.Alternatively, by obtaining the space correlation between thetransmission antennas using the channel matrix H, it may sufficiently bedecided to perform beamforming if the correlation value is high. Todecide strictly, it may also be possible to decide using the channelmatrix H.

As an example, a 2×2 channel matrix H is shown in expression (10).

$\begin{matrix}\lbrack 12\rbrack & \; \\{H = \begin{bmatrix}h_{11} & h_{12} \\h_{21} & h_{22}\end{bmatrix}} & (10)\end{matrix}$

The CQI information calculated and fed back in the receiver on thereceiving station side is generated on the basis of the SINR of eachtransmission antenna ANT1, ANT2, and largely depends on the square normof the column vector of the channel matrix H representing the spacepropagation condition of each transmission antenna. As an example, thespace condition of the transmission antenna ANT1 is represented byexpression (11).

[13]

k ₁ =|h ₁₁|² +|h ₂₁|²   (11)

In contrast, as a solution obtained from expressions (7), (8), a squareof the largest value among the singular values of the solution obtainedby performing singular value decomposition (SVD) on the H matrixsignifies the space propagation condition when being beamformed by aplurality of transmission antennas.

Expression (12) shows the solution of SVD, and expression (13) shows aparameter corresponding to expression (11).

$\begin{matrix}\lbrack 14\rbrack & \; \\{H = {\begin{bmatrix}h_{11} & h_{12} \\h_{21} & h_{22}\end{bmatrix} = {{U\begin{bmatrix}\sqrt{\lambda_{1}} & 0 \\0 & \sqrt{\lambda_{2}}\end{bmatrix}}V^{H}}}} & (12) \\{k_{total} = {\max \left( {\lambda_{1},\lambda_{2}} \right)}} & (13)\end{matrix}$

Additionally, in regard to the spatial correlation described earlier, ifthe correlation is high, a ratio between the largest singular value andother singular values becomes greatly different from 1. Here, using theratio between expression (11) and expression (13), an SINR to beobtained when the beamforming is performed is estimated and thenconverted into CQI, and thus, a transmittable data amount can bedetermined.

Through such the processing process, to AMC set section 101, MIMOmultiplexing/beamforming selection and AMC setting are specified, andMAS selection is determined.

First, a case when the MIMO multiplexing is selected is described, and acase when the beamforming is selected follows next.

When the MIMO multiplexing is selected, based on the CQI information fedback on the basis of each transmission antenna, a data amounttransmittable by each transmission antenna is distributed by means of adata S/P conversion section 104. Next, coding is performed in encoders105 a, 105 b so as fit to each transmission data stream, and modulationis made in modulators 106 a, 106 b.

The outputs of modulators 106 a, 106 b are weighted in weightingcircuits 107 a, 107 b, respectively, with the same fixed value as atransmission weight, so as to generate the data channel. Here, in caseof the value by which the power is normalized with the number oftransmission antennas N,

[15]

1/√{square root over (N)}

may be weighted.

When the beamforming is selected, coding is performed by an encoder 105c and modulation is performed by a modulator 106 c, each being fit to asingle data stream. Then, the output data of modulator 106 c is copiedin a reproducer 108, and a data channel is generated by weighting thetransmission weight Wtx of the ZF solution, obtained from the channelmatrix H of the feedback information in weighting circuits 107 a, 107 b,corresponding to each transmission antenna ANT1, ANT2.

Next, the data channel is orthogonally multiplexed with another channelin a parallel-to-serial (P/S) conversion sections 109 a, 109 b.

Additionally, as to a pilot channel A, a specific pattern to thetransmitting station is generated in a pilot generation section 120.Then, after controlled to orthogonalize between the transmissionantennas in an orthogonalizing circuit 121, the pilot channel A isgenerated by performing modulation known in the receiving station inmodulation sections 122 a, 122 b.

On the other hand, a scheduler management channel B, after the contentspecified by scheduler 100 is arranged in a scheduler managementinformation generation section 102, in modulation sections 123 a, 123 b,the scheduler management channel B is generated by performing modulationknown in the receiving station. Next, the channel orthogonallymultiplexed in parallel-to-serial (P/S) conversion sections 109 a, 109 bare up-converted to carrier frequencies in transmission RF sections 124a, 124 b, and radiated from the antennas ANT1, ANT2.

Now, the configuration of the above scheduler 100, MIMOmultiplexing/beamforming selection & AMC set section 101 and schedulermanagement information generation section 102 are described in moredetail.

FIG. 12 shows a diagram explaining input information to scheduler 100.Also, FIG. 13 shows an exemplary configuration of scheduler 100.

In FIG. 12, a state that a certain user i desires a frequency domain 3.At that time, there are conveyed CQI information when using the MIMOmultiplexing, CQI information when using the beamforming, transmissionand reception weight in formation Wtx, Wrx reported by scheduler 100,and further, ACK/NACK and QoS information as common information.

Here, as will be apparent from other embodiments described later, it ispossible that the weight information may be the transmission weightinformation Wtx only.

Also, the QoS information is transmission priority determined from atransmission signal type such as voice, packet, etc. and a data amountretained in the transmission queue, and is managed by the upper layer ofthe transmitting station, and reported therefrom.

As shown in FIG. 12, another user j also issues a communication requestin the same frequency domain 3, which is in an information inputcondition of the desire of using the frequency domain 3 as the secondinput number of persons (number of users). Corresponding thereto,scheduler 100 includes a plurality of schedulers 1-n as shown in FIG.13, into which QoS information A of a user desiring the correspondingfrequency domain is input, and also, feedback information B from thereceiving stations of the users desiring the corresponding frequencydomains is input. Based on the above information collected from theplurality of users, the most appropriate user selection is performed onthe frequency-by-frequency basis. As to the methods of the above userselection, for example, it is possible to apply a technique described inTR25.848 of the 3GPP documents, such as RR (Round Robin) method,(Proportional Fairness) method and Max-CIR method.

Next, with attention directed to the frequency domain 3, description ismade according to the processing flow shown in FIG. 14. First, userfeedback information selected and to be fed back from the receivingstation is regenerated in feedback information reception section 110 andforwarded to MIMO multiplexing/beamforming selection & AMC set section101 (step S1).

MIMO multiplexing/beamforming selection & AMC set section 101discriminates information necessary for the MIMO multiplexing frominformation necessary the beamforming (step S2), and after thediscrimination, adds an ID to identify the selection of either the MIMOmultiplexing or the beamforming (steps S3 a, 3 b), and calculatestransmission information amount depending on each selected case (stepsS4 a, 4 b).

Here, in the MIMO multiplexing, in order to transmit different datastreams from the respective antennas, for example, when there are twotransmission antennas, two CQI exist. On the other hand, in thebeamforming, only one CQI exists because the same data stream istransmitted from the entire antennas with the phases varied by theweights.

Thus, a calculated throughput is obtained in the following manner.

In case of the MIMO multiplexing;

$\begin{matrix}\lbrack 16\rbrack & \; \\{\sum\limits_{i}{{trans}\left\lbrack {{CQI}_{MIMO}(i)} \right\rbrack}} & (14)\end{matrix}$

In case of the beamforming;

[17]

trans[CQI_(BF)(0)]  (15)

In the above expression (14), “i” denotes an antenna i, and since thebeamforming has only CQI for the entire antennas, a notation of 0 isshown. Also, “trans” signifies transformation from CQI to atransmittable information amount. By comparing the transmissioninformation amount obtained from expressions (14), (15) (step S5), themethod which can convey larger information amount is selected (step S6).As a tendency, the MIMO multiplexing comes to be selected in thevicinity of a transmitting station having a good propagationenvironment, and the beamforming comes to be selected in a cell edgehaving a bad propagation environment.

Next, according to the information of the selected system, the selectionof the MIMO multiplexing and the beamforming and an AMC commandcorresponding thereto are reported to each module (step S7).

At the same time, the above information is reported to schedulermanagement information generation section 102 (step S8). Then, afterbeing added to the scheduler management channel format shown in FIG. 3in scheduler management information generation section 102, theinformation is reported to the receiving station (step S9).

Namely, in the scheduler management channel, according to the ID of theselected system, the MIMO multiplexing/beamforming designation isselected, and the AMC information is reflected in the respectivesystems, using the format shown in FIGS. 4, 5.

[Receiving Station]

In FIG. 11, a signal transmitted from the transmitting station isdown-converted into a baseband in reception RF sections 200 a, 200 b,and then, in S/P conversion sections 201 a, 201 b, the orthogonalmultiplexed channels are separated. As described earlier, the S/Pconversion is applied because of being orthogonally time-multiplexed asan example, and however, it is possible to cope with other orthogonallymultiplexed cases.

Using the separated pilot channel A, a propagation path variation isobtained in a channel estimation section 202.

At the same time, the demodulation of other channels is performed in ademodulation section 203, and feedback information is generated in afeedback information generation section 220.

To demodulate a data channel C, it is necessary to know informationabout adaptive modulation, and therefore, first, it is necessary todemodulate the scheduler management channel B. Since the modulationsystem of the scheduler management channel B is known in the receivingstation, it is possible to demodulate the scheduler management channel Bin demodulation section 203 by means of an MLD algorithm, etc., usingthe channel estimation value estimated from the pilot channel A.

The demodulated information of the scheduler management channel B isconfirmed in a scheduler management information decision section 204,and a demodulation decision is made in a demodulation decision section205 by deciding whether there is a data destined to the self-station inthe present frame. The reason is that, if there is no data destined tothe self-station, an effect of reducing power consumption in thereceiving station is obtainable by omitting the demodulation operation.

Next, when there is a data destined to the self-station, MAS selectionis decided in an MAS selection circuit 206 from the information of thescheduler management channel B, and a demodulation algorithm isseparated according to the case of either MIMO multiplexed orbeamformed.

First, demodulation and decoding in the case of the MIMO multiplexingare described, and thereafter, demodulation and decoding in the case ofthe beamforming are described.

Using the channel estimation value estimated from the pilot channel A,the MIMO multiplexed signal is demodulated in a demodulation section 207by means of an MLD algorithm, etc., after the modulation information isknown from the scheduler information.

After being demodulated, a signal for each transmission antenna isextracted, and coding information thereof on a stream-by-stream basiscomes to be known from the scheduler information, and then, decodingcorresponding thereto is performed in decoders 208 a, 208 b. By this,data streams are obtained, and the original data sequence is obtained byperforming P/S conversion of the output of decoders 208 a, 208 b in aP/S converter 209. Finally, a decision whether the data has beentransmitted correctly is made in a retransmission decision circuit 210.

The above decision in retransmission decision circuit 210 may beperformed by an error decision using addition of CRC (cyclic redundancycheck) information which has also been used conventionally. Here, theretransmission decision has been made after the data is rearranged bythe P/S conversion in P/S converter 209. Instead, it is also possible tocope with by performing retransmission decision on the basis oftransmission data stream, as will be described later.

On the other hand, to a beamformed signal, a reception antenna weight211 of a ZF solution, calculated in advance in the transmitting station,is obtained from scheduler management information decision section 204,weighting thereof is performed. Thus, signal synthesis between theantennas is performed in an antenna synthesis section 212, and channelcompensation is made in a demodulation section 213.

Then, in demodulation section 213, modulation information is known fromthe scheduler management information obtained from scheduler managementinformation decision section 204, and demapping corresponding to themodulation system thereof is performed. After demodulation through thedemapping, coding information is obtained from scheduler managementinformation decision section 204, and corresponding decoding isperformed in a decoding section 214. By this, a data is obtained, andfinally, whether the data has been transmitted correctly is decided inretransmission decision section 210.

When retransmission decision section 210 decides that retransmission isnot necessary, the data is output, and an ACK is returned as thefeedback. When the retransmission is necessary, a NACK is returned.Also, when there is provided a retransmission function of highfunctionality, such as HARQ (hybrid auto-repeat request: a technique toenhance reception accuracy by utilizing a formerly transmitted signal atthe time of retransmission), it may also be possible to store into atemporary buffer, not discard the received signal, and to synthesize atthe time of next retransmission, thereby improving the receptionquality.

Feedback information is generated in a feedback information generationsection 220. For this purpose, as an output from channel estimationsection 202, a channel matrix H 221 is obtained from the channelestimation value, and also SINR on the basis of each transmissionantenna is calculated in an SINR calculation section 222. Then, CQIinformation, which is obtained in a CQI conversion section 223 throughthe CQI conversion of the above calculation result on the basis of eachtransmission antenna, and the above ACK/NACK decision output areconverted in a feedback information conversion section 215 into feedbackinformation, and given as ACK/NACK information 224.

In the SINR calculation, the calculation is made by obtaining acalculation result from expression (11) in regard to the calculation ofa signal S, and also, in regard to noise N, by obtaining the dispersionof an instantaneous channel estimation value to an average channelestimation value in a short-time interval on the basis of each receptionantenna.

Finally, feedback information arranged as feedback information 225 ismodulated in a modulation section 226 with a predetermined modulationsystem. On the other hand, a separate pilot fed from a separate pilotchannel generation section 227 is modulated in a modulator 228. Theabove two modulation outputs are orthogonally time-multiplexed in a P/Sconversion section 229, up-converted into a carrier frequency in atransmission RF section 230, and then radiated from the antenna.

In FIG. 11, in regard to a link from the receiving station toward thetransmitting station, the figure is illustrated in the form oftransmitting from a single antenna ANT for simplification. However, itis also possible to cope with a method of transmitting using a pluralityof antennas implemented on the receiving station.

Additionally, in the figure of the receiving station, each line havingan added oblique line signifies that information flows in parallel.

Embodiment 2]

Next, an embodiment 2 corresponding to the group 2 in Tables 1, 2 isdescribed. FIGS. 15 and 16 show exemplary configurations of atransmitting station and a receiving station, respectively,corresponding to the embodiment 2.

[Transmitting Station]

In FIG. 15, description is made with attention directed to the points ofdifference from the transmitting station according to the embodiment 1shown in FIG. 10. The feature of the transmitting station correspondingto the embodiment 2 shown in FIG. 15 lies in that only information isreflected in scheduler 100 when the ZF solution is obtained from thechannel matrix H fed back from the receiving station.

Also, because of a configuration reporting only the transmission weightW_(tx), it is different from the embodiment 1 in that a weight reportedfrom scheduler management information generation section 102 isperformed using W_(tx).

[Receiving Station]

Corresponding to the above modification in the transmitting station, theconfiguration of the receiving station is also different. According tothe configuration of the receiving station in the embodiment shown inFIG. 11, when the beamforming is selected, the reception weight Wrx isreported using the information from scheduler management informationdecision section 204, and by the adaptation thereof, it was possible toperformed antenna synthesis by means of the pseudo ZF solution 211.

In contrast, according to the embodiment 2 shown in FIG. 16, since thetransmission weight Wtx is reported from scheduler managementinformation decision section 204, using the channel estimation valueobtained in channel estimation section 202 from the pilot channel A andthe above transmission weight Wtx, an MMSE solution obtained from theaforementioned expression (9) is obtained in an MMSE solutioncalculation section 211 a.

It is configured that the antenna synthesis is made using the abovereception weight. As compared with the method of the group 1, acalculation amount in the receiving station increases to some extent.However, it is possible to improve the characteristic because channelvariation deterioration caused by a feedback delay and noise emphasis iseliminated.

Embodiment 3

An embodiment 3 corresponding to the group 3 shown in Tables 1, 2 isdescribed. FIGS. 17 and 18 show exemplary configurations of atransmitting station and a receiving station, respectively,corresponding to the embodiment 3.

[Transmitting Station]

As compared to the embodiment 2, in the embodiment 3, there is adifference only in the point that the information to be fed back is notthe channel matrix H but a transmission weight (Wtx) 115 d. As animproved point, the information amount to be fed back can be reduced.Also, as an advantageous point, it is also possible to point out thatthe calculation amount in the transmitting station can be reduced.

[Receiving Station]

In the receiving station, as contrasted with the receiving stationconfiguration of the embodiment 2 shown in FIG. 16, there is adifference in that, in regard to the information to be fed back, a ZFsolution 231 obtained from the channel matrix H 221 by use ofexpressions (7), (8) is calculated, and the transmission weight Wtx isfed back. This will increase the calculation amount in the receivingstation, and however, the information amount to be fed back is reduced,and corresponding to the above amount, it is possible to generate anarea to be allocated to a data channel from the receiving station to thetransmitting station.

Embodiment 4

An embodiment 4 corresponding to the group 4 shown in Tables 1, 2 isdescribed. FIGS. 19 and 20 show exemplary configurations of atransmitting station and a receiving station, respectively,corresponding to the embodiment 4.

[Transmitting Station]

As contrasted with the transmitting station configuration of theembodiment 3 shown in FIG. 17, in the transmitting station according tothe embodiment 4, the information to be fed back is not the transmissionweight Wtx, but a transmission direction 115 e. It is an improved pointthat the reduction of the information amount to be fed back can beattained. In regard to the above transmission direction 115 e, a peakvalue in the beam pattern of the transmission weight in the ZF solutionobtained from expressions (7), (8) is used, and further, by quantizingas shown in FIG. 9, the feedback amount can be reduced. In addition,when the transmission direction 115 e is received as feedbackinformation, a beam pattern is generated so that the power isconcentrated maximally to the direction concerned. An appropriatetransmission weight (Wtx) 115 d is generated and reported to scheduler100

[Receiving Station]

In the receiving station, as contrasted with the receiving stationconfiguration of the embodiment 3 shown in FIG. 18, a transmissionweight Wtx of ZF solution 231 is obtained as feedback information, andthereafter, a peak value (θ) of transmission direction 232, to which thepower of the beam pattern generated by the above weight is concentrated,is obtained and fed back.

Embodiment 5

An embodiment 5 corresponding to the group 5 shown in Tables 1, 2 isdescribed. FIGS. 21 and 22 show exemplary configurations of atransmitting station and a receiving station, respectively,corresponding to the embodiment 5.

[Transmitting Station]

The transmitting station corresponding to this embodiment 5 shown inFIG. 21 is an example of switching between the MIMO multiplexing and thebeamforming by means of TDD. As compared with the transmitting stationof the embodiment 1 shown in FIG. 10, a feature is that a channelestimation value from the receiving station to the transmitting stationis obtained in channel estimation section 113, and based on the aboveestimated value, power difference between the transmitting station andthe receiving station is corrected in a power correction circuit 117, soas to generate a channel matrix 118 from the transmitting station to thereceiving station. Next, as a feature, the reception weight Wrx of thereceiving station is generated by obtaining a ZF solution 119 using thegenerated channel matrix 118.

Because of TDD using the same frequency band, it is possible to estimatethe propagation path characteristic on one side using a propagation pathcharacteristic on the other side if a link switchover from thetransmitting station to the receiving station and a link switchover fromthe receiving station to the transmitting station are made so as tosufficiently track to the fading. By this, it is possible to make thefeedback information amount necessary for transmission beamforming zero.

[Receiving Station]

As contrasted with the receiving station configuration of the embodiment1 shown in FIG. 11, the receiving station does not require the feedbackinformation excluding CQI and ACK/NACK information 224. However, insteadof feeding back the information of the channel matrix H, anorthogonalization section 227 a is provided for orthogonalizing separatepilot channels generated in a separate pilot channel generation section227 from the entire antennas provided in the receiving station. Theorthogonalized separate pilot channels are transmitted to the entireantennas (two antennas in FIG. 22) provided in the receiving station.

Additionally, as to the feedback information, it may be possible totransmit from one antenna, or the entire antennas may be used. However,as a different point, as to the separate pilot, it is necessary toorthogonalize and transmit from the entire antennas.

Embodiment 6

An embodiment 6 corresponding to the group 6 shown in Tables 1, 2 isdescribed. FIGS. 23 and 24 show exemplary configurations of atransmitting station and a receiving station, respectively,corresponding to the embodiment 6.

[Transmitting Station]

As contrasted with the transmitting station of the embodiment 5 shown inFIG. 21, a feature lies in a point that only the transmission weight Wtxinformation is reflected in multi-user scheduler 100 when obtaining ZFsolution 119 of channel matrix H 118 obtained from the channelestimation value of the separate pilot channel from the receivingstation to the transmitting station.

Also, because of reporting only the transmission weight Wtx, the weightto be reported in scheduler management information generation section102 is reported using Wtx.

[Receiving Station]

As contrasted with the receiving station configuration of the embodiment5 shown in FIG. 22, as a different point, the receiving station obtainsan MMSE solution 216 when the beamforming is specified in MAS selectionsection 206. Further, as a feature of the receiving station shown inFIG. 22, there is applied the same content described as the point ofdifference in the receiving station of the embodiment 2 shown in FIG. 16from the receiving station of the embodiment 1 shown in FIG. 11.

Here, in the aforementioned embodiments 1 through 6, in regard to thetransmission data stream of the MIMO multiplexing, the description hasbeen made in such a mode as retransmitting on a block-by-block basis ofa single transmission opportunity for the entire antennas.

However, it may also be possible to performing retransmission control onthe basis of each data stream of the antenna. In this case, in FIG. 25illustrating the configurations of the demodulation section 213 andthereafter of the receiving station, the configurations of the decodingsection and thereafter are required correspondingly to the respectiveantennas. Number information of each antenna corresponding to feedbackinformation conversion sections 215 a, 215 b is input. Then, in amultiplexing section 217, feedback information in regard to the entireantennas is multiplexed and output.

INDUSTRIAL APPLICABILITY

As having been described above, according to the present invention, itis possible to obtain a concrete configuration by making full use of thetechnical features of the MIMO multiplexing and the beamforming,enabling instantaneous switching of the both by devising the commonscheduler management channel using a single common pilot only.

Additionally, in the above description of the embodiments, the MIMOmultiplexing and the beamforming are exemplified, and however, using thesimilar device, it is also possible to develop to switchover among MIMOmultiplexing, coded transmission diversity, and beamforming, etc.

1. A transmitting station in the radio system performing scheduledtransmission to a plurality of user terminals comprising: a plurality ofantennas; a reception unit configured to obtain reception qualityinformation estimated from a pilot channel among information fed backfrom each of the plurality of user terminals, to determine based on theobtained reception quality information, a transmission system for theplurality of antennas; and a transmission unit configured to add aspecific bit which identifies the determined transmission system to ascheduler management channel, and to vary contents of the other bit areain the scheduler management channel, as corresponding to the specificbit, and further transmit the scheduler management channel to theplurality of user terminals.
 2. The transmitting station in the radiosystem according to claim 1, wherein when the determined transmissionsystem is beamforming, the transmitting station reports weightinformation to the plurality of antennas or weight information of aplurality of reception antennas, using the other bit area.